This invention relates to ink jets of the type which emit droplets of ink, and more particularly, to impulse ink jets of the type which emit droplets of ink on demand.
Impulse or demand ink jets emit or eject droplets of ink from an orifice in response to the movement of a transducer associated with a chamber coupled to the orifice. The transducer may be of the piezoelectric type which upon energization contracts the volume of the chamber so as to emit a droplet of ink from the orifice. An ink jet of this type is disclosed in U.S. Pat. No. 3,683,212--Zoltan wherein the chamber is formed by a glass tube which is substantially surrounded by a cylindrical transducer. The orifice coupled to the chamber may be formed, at least in part, by the glass tube. As the cylindrical transducer contracts in response to energization, the volume of the chamber contracts and a droplet of ink is expelled from the orifice.
Impulse ink jets formed from glass tubes and cylindrical transducers are typically difficult to construct with reproducibility, i.e., achieving repeatable characteristics in different ink jets. Moreover, the cylindrical transducer is somewhat expensive and fair amounts of electrical energy are needed to energize the transducer so as to contract the volume of the glass tube sufficiently to produce a droplet. In addition, relatively large amounts of energy are dissipated by mechanical damping. Ink jets utilizing this cylindrical construction are also difficult to assemble. Moreover, ink jets of this type have a substantial number of significant resonances which complicate behavior of the jet. In addition, ink jets of this type are difficult to construct in a compact array.
Other impulse ink jet designs have been employed including composite structures in which a chamber coupled to an orifice is formed in part by a substantially planar diaphragm which is deflected inwardly into the chamber by a suitable transducer. Such impulse jet constructions are disclosed in U.S. Pat. Nos. 3,988,745--Zoltan, 4,115,789--Fischbeck and 4,032,929--Fischbeck et al. Although constructions of this type are desirable from a reproducibility and cost standpoint, as well as from energy considerations, such devices may create serious material compatibility problems. In this regard, it will be understood that a variety of materials may contact the ink and this may create ink and materials compatibility problems.